[PATCH] edia: dvbdev: fix a use-after-free

[Zhipeng Lu <alexious@xxxxxxxxxx>]

In dvb_register_device, *pdvbdev is set equal to dvbdev, which is freed
in several error-handling paths. However, *pdvbdev is not set to NULL
after dvbdev's deallocation, causing use-after-frees in many places,
for example, in the following call chain:

budget_register
  |-> dvb_dmxdev_init
        |-> dvb_register_device
  |-> dvb_dmxdev_release
        |-> dvb_unregister_device
              |-> dvb_remove_device
                    |-> dvb_device_put
                          |-> kref_put

When calling dvb_unregister_device, dmxdev->dvbdev (i.e. *pdvbdev in
dvb_register_device) could point to memory that had been freed in
dvb_register_device. Thereafter, this pointer is transferred to
kref_put and triggering a use-after-free.

Fixes: b61901024776 ("V4L/DVB (5244): Dvbdev: fix illegal re-usage of fileoperations struct")
Signed-off-by: Zhipeng Lu <alexious@xxxxxxxxxx>
---
 drivers/media/dvb-core/dvbdev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/media/dvb-core/dvbdev.c b/drivers/media/dvb-core/dvbdev.c
index 305bb21d843c..a027b9110793 100644
--- a/drivers/media/dvb-core/dvbdev.c
+++ b/drivers/media/dvb-core/dvbdev.c
@@ -488,6 +488,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		dvbdevfops = kmemdup(template->fops, sizeof(*dvbdevfops), GFP_KERNEL);
 		if (!dvbdevfops) {
 			kfree(dvbdev);
+			*pdvbdev = NULL;
 			mutex_unlock(&dvbdev_register_lock);
 			return -ENOMEM;
 		}
@@ -496,6 +497,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		if (!new_node) {
 			kfree(dvbdevfops);
 			kfree(dvbdev);
+			*pdvbdev = NULL;
 			mutex_unlock(&dvbdev_register_lock);
 			return -ENOMEM;
 		}
@@ -529,6 +531,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		}
 		list_del(&dvbdev->list_head);
 		kfree(dvbdev);
+		*pdvbdev = NULL;
 		up_write(&minor_rwsem);
 		mutex_unlock(&dvbdev_register_lock);
 		return -EINVAL;
@@ -551,6 +554,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		dvb_media_device_free(dvbdev);
 		list_del(&dvbdev->list_head);
 		kfree(dvbdev);
+		*pdvbdev = NULL;
 		mutex_unlock(&dvbdev_register_lock);
 		return ret;
 	}
@@ -569,6 +573,7 @@ int dvb_register_device(struct dvb_adapter *adap, struct dvb_device **pdvbdev,
 		dvb_media_device_free(dvbdev);
 		list_del(&dvbdev->list_head);
 		kfree(dvbdev);
+		*pdvbdev = NULL;
 		mutex_unlock(&dvbdev_register_lock);
 		return PTR_ERR(clsdev);
 	}
-- 
2.34.1